A period of absence from employment with the state, county, or city occurring either during a war involving the United States or in any other national emergency and for 90 days thereafter for one of the following reasons is considered as service for the purpose of determining the number of years of employment used in calculating vacation leave credits under this section:
(1) having been ordered on active duty with the armed forces of the United States;
(2) voluntary service on active duty in the armed forces or on ships operated by or for the United States government; or
(3) direct assignment to the United States department of defense for duties related to national defense efforts if a leave of absence has been granted by the employer.